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Scientist map gene for leprosy in Vietnamese families
By Adam Marcus

A gene that predisposes people to leprosy has been mapped to chromosome 6, and researchers are close to identifying the gene. It may be the first susceptibility gene associated with two forms of the disfiguring disease.

"We know pretty well where the gene is," says Erwin Schurr, a geneticist at McGill University in Montreal, Canada, who led the study of families in Viet Nam. The gene, he adds, predisposes people to either mild or severe disease.

Rembrandt van Rijn: Portrait of an Oriental. Art historians believe this painting depicts the Biblical King Uzziah, who was stricken with leprosy for usurping the authority of the Temple priests. c. 1639

Previously, researchers had located possible susceptibility genes for leprosy in Indian families. But those genes lie on chromosomes 10 and 20 and appear to involve the less-severe form of leprosy.

Leprosy is caused by prolonged contact with Mycobacterium leprae. The bacterium, whose genome was sequenced in 2001, is related to the pathogen that causes tuberculosis. Schurr plans to investigate a link between having the leprosy-susceptibility gene and the risk for contracting tuberculosis.

Leprosy has been called the "least-contagious contagious disease" because only one person in 10,000 exposed to the pathogen will contract the disease. Robert Modlin, a leprosy expert at the University of California, Los Angeles, School of Medicine, says finding susceptibility genes could help researchers understand why this is so.

One factor appears to be the type of immune response the bacteria provokes in a person. In some people, the reaction is inexplicably inadequate. "Why does the immune system of some patients decide to make an incorrect choice?" Modlin asks. "It would be interesting to know if that's pre-programmed genetically, but it could be due to other factors" such as the dose of bacteria in the infection, the type of exposure, or the person's health when infected.

In the new study, published in Nature Genetics, the researchers used DNA from 86 Vietnamese families, including 205 siblings with leprosy. Having an affected sibling doubled a person's risk for the disease, the researchers found. Some 700,000 new cases of leprosy are reported each year, mostly in India, Africa and South America.

Since scientists discovered in 1873 that M. leprae causes leprosy—then known as Hansen's disease after the doctor who identified the microbe—no one has been able to grow it in the laboratory. For the sequencing project, the researchers grew the bacterium in an armadillo.

See related GNN article
»Genome of bacterium that causes leprosy is sequenced

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Mira, M. et al. Chromosome 6q25 is linked to susceptibility to leprosy in a Vietnamese population. Nat Genet Published online February 10, 2003.

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